• Resolved

ISO124: iso124 not working as expected

Part Number: ISO124

I breadboard an iso124 circuit and 2 TI dcpo1b 15v supplies. I double checked my connections.

I am using the plastic .1 gridded breadboard for thi prototype.  - Is this possibly the problem?

I noticed in the app note that "no conductive materia ie traces can be undeneath the chip.

Along that same line how far away does the chip have to be from say a metal enclosure.

  • Hi Michael,

    Welcome to our e2e forum!  When you say the ISO124 is not working as expected, can you describe what you mean?  What are you expecting and what are you seeing?  Those plastic squeeze boards can be problematic, especially if they are old.  Spacing will be dependent on your application.

     

    Regards,

    Tom

  • In reply to Tom Hendrick:

    Thanks for the quick response. I am using the circuit to isolate a DC signal. On the bench this a 5v supply. going to Vin refenced to high side ground. I am expecting the same DC signal at Vout refenced to low side ground. Any input 0 5v and output is stuck at 8.3v. I beleive my breadboard is ok , new but I am concerned with the metal being under the chip since a point was made in the app note, not to run any tracesunder the chip. Thanks
  • In reply to Michael Stadtler:

    Hi Michael,

    Can you give me a part number for the 15V supplies you are using?  The app note regarding traces running under the chip is probably not something you need to worry about at this point in your debug process.  Traces that run under the chip between the HV side and LV side will essentially reduce the creepage and clearance distance, which will in turn impact the isolation voltage.  The metal strips in the squeeze board do have the same impact as traces, but you don't really seem to be dealing with any high voltage at the moment.

     

    Regards,

    Tom

  • In reply to Tom Hendrick:

    Hello again,

    DCP011512DBP-ND                  IC REG ISOLATED +/-12V 41MA 7DIP  are the 2 PS chips.

    You are correct re: high voltage - this circuit is not.

    I'll try a new ISO24 device next I think and maybe a perfboard wired prototype.

    Thanik

  • In reply to Michael Stadtler:

    OK - the isolated power supply chips should be fine. If you can draw up a schematic of your connections, I'd be happy to review them as well.

     

    Regards,

    Tom

  • In reply to Tom Hendrick:

    This circuit show a +24v supply, I will use in the final version.  I am using +15v currently since I don't have the correct chips for +24v.

    I am using a 0-7v DC supply for Vin with reference to ACOM  U1-16.

    Thanks again

  • In reply to Michael Stadtler:

    What decoupling caps should I use on the +24 input 1uf or .47uf?
    What decoupling caps should I use on the +/- 12v output 1uf or .47uf?
  • In reply to Michael Stadtler:

    Hi Michael.

    By the DCP011512DBP datasheet, 1uF on the input voltage and 0.47uF on the outputs.

     

    Regards,

    Tom

  • In reply to Tom Hendrick:

    Getting back to this design, was on another project.

    The data sheet (below)  reccomends .47uf for the 24v input part that I have. I only have 1uf caps will they work until I can get the .47uf.   I realize they are just  input capacitors, but I don't want to damage these parts.

    For 5-V to 15-V input devices, a 2.2-μF, low-ESR ceramic capacitor ensures a good startup performance. For 24- V input voltage devices, 0.47 μF ceramic capacitors are recommended. Tantalum capacitors are not recommended, since most do not have low-ESR values and will degrade performance. If tantalum capacitors must be used, close attention must be paid to both the ESR and voltage as derated by the vendor.